In general the invention will be discussed in relation to the placement of prostheses in the aorta in the region known as the thoracic arch where the aorta leaves the heart and curves over in approximately a semi-circle to the descending aorta and then into the abdominal aorta and then into the lower limbs via the iliac arteries. The invention is, however, not so restricted and can relate to placement of prostheses within or in place of lumens in any portion of a human or animal body.
Aortic aneurysms can occur high up in the thoracic aorta and in this region the aorta is curved and placement of a substantially cylindrical prosthesis in such a curved region can cause problems. The upper end of the prosthesis may not attain close apposition to the vessel wall. This can result in the lumen of the prosthesis being closed off or reduced in lumen diameter. Kinks can also occur along the length of the prosthesis and these can cause problems with restriction of flow in the lumen.